Iron-nickel-copper alloy



Patented May 12, 1931 UNITED STATES PATENT OFFICE NORMAN B. FILLING-,OF ELIZABETH, NEW JERSEY, ASSIGNOR TO THE INTEBhl'ATIONAI NICKEL COMPAN Y, INCL, A. CORPORATION OF DELAWARE nickel and copper, it ife not intended to be restricted to the partid ar ones shown, ex-

Ill'o Drawing.

mon-nrcxaL-corrna Armor Thisin-vention relates to ferrous nickel alloys and particularly to iron-nickelcopper alloys whichare characterized by the property 01: resistance to corrosion.

,An object of this inventioiris to provide an alloy of this type resistant to corrosion by atmospheric and other agenciesand which is capable of being readily worked and adapted for a wide variety of uses.

These and other desired objects and advan tages of the invelltion will be described in the following specification, certain preferred combinations being iven by way of illustration, but since the uh erlying principles apply to a wide range proportions of iron,

cept as 'such restrictions re clearly imposed by the appended claims.

As is well'known, iron, and iron containing as much as several percent of alloyed elements, is extremely subject to corrosion by atmospheric agencies,-a coating of hydrated iron oxide, commonly known as. rust, forming under the combined influence of moisture, oxygen and other gases usually resent in the atmosphere. Such a coating 0 rust is loose, flaky and porous, and is not protective but may even accelerate further corrosion by its screening action, setting up the wellknown electrolytic oxygen concentration cells.

The addition of large amounts of nickel to iron lessens the rate of such corrosion but does not change in any substantial way the nature of the rust coating formed. Even iron-nickel alloys containing 80% of nickel will rust on exposure to moist air containing traces of sulphurous gases. The rust coatin thus vformed is thin but flaky, readilys litting off from the surface, or spelling, and corrosion proceeds at a slow rate but unchecked. With intermediate contents of nickel, as or the flaky, non-protective type of rust coating forms, with corrosion rates about proportional tot-he iron content. a

I have by the pronounced flaking properties and found that the addition of copper. to'iron-nickel alloys has a marked effect on the physical structure of the-corrosion prodnot formed on atmospheric exposure, where- Application filed November 16, 1928. Serial No. 319,998..

very substantial reduction in the total'non- "ferrous content to obtain an. equivalent degree of atmospheric corrosion resistance. As concrete examples, an exposure test conducted in the open air for a period of several.

years showed that an iron-nickel-copper alloy containing 25% nickel, 5% copper, was equal in durability to an iron-nickel alloy containing 50% nickel; again, an iron-nickel-copper alloy containing 50% nickel 9% copper, was the equivalent of an iron-nickel alloy containing 80% nickel. These examples show the economy which the addition of copper to iron-nickel alloys permits. Y

The alloys of the present invention comprise compositions containing the "following elements in substantially the proportions enumerated, viz: .nickel, .1279%;- copper, 1-32%; iron, 20-87%; and carbon, .012%.

The nickel shouldbe equal to or greater than 7 one and one-half times the copper content. In practice the nickel content should. not be less than 1.85 times the copper'content to. in sure homogeneity of the alloy. Carbon,-in the case of compositions in which the ratio of nickel content to the-nickel plus iron con.

tent is less than .27,'is defined as follows:

Where G equals the percentage of carbon present, N equals the percentage of nickel, and F equals the percentage of iron. Silicon, manganese and other elements commonly ,used to aid in securing sound, malleable ingots may be present.

The alloys comprised within the above.

- has been noted in many dilute non-oxidizing acids and in various salt solutions.

As an example of this, the iron-nickel alloy with 38% nickel has a corrosion rate in 5% aerated sulphuric acid of 860.milligrams per square decimeter per day; the

substitution of 5% of copper for an equal amount of nickel lowered this rate to 550 milligrams. Again, the iron-nickel alloy with nickel has a similar corrosion rate of 660 milligrams, and the addition to this alloy of'8% copper (displacing iron) lowered the'corrosion rate to340milligrams.

In general, the hardness and strength properties do not vary to any substantial amount in going from one extreme of composition to another, but the corrosion resistance does, and alloys lying in the higher ranges of iron contents .will have a much lower resistance to corrosion than those lying within the low iron ranges; there is no sudden change in order of magnitude, but a gradual, continuous, increasing degree of corrosion resistance as the nickel content or the copper content is increased. On the other hand, certain properties do change greatly within these limits, requiring a restriction of com osition to gain certain ends. The'hot mallea ility is largely a matter of copper content, and alloys containing more than 12% of copper are forgeable and otherwise workable only with much difiiculty. Although showing a high degree of resistance to corrosion, they are of value chiefly in the form ,of castings. When articles shaped by working are required, itis preferable to have theropper content less than 12%, and when the highest degree of malleability and ductility isrequired, I limit the. copper content -,to- 6%. malleability of nickel alloys disclosed in my The process for improving the co-pending application, Serial Number 223,233, filed September 30, 1927 is of materialservice.

Some of these alloys are non-magnetic, and these are defined as having the ratio of the nickel content to the nickel plus iron anceiwithl the rule made in an earlier pararesistance, with a substantially non-magnetic conditlon. When the nlckel-iron who is more than .30, the alloys are normally magnetic at room temperature and display magnetic critical points at higher temperatures analogous to the reversible iron-nickel alloys. 7 7

' Some of these alloys have low coefficients of thermal expansion in addition to the other characteristics of the main group. These are those alloys having copper ranging from 112%, with the ratio of the, nickel content to the nickel plus iron contents greater than .30 and less than $42. In general nature, these resemble the corresponding nickel-iron alloys. Copper increases the expansivity for a given nickel ratio, but a coeflicient of .000003 per C., coupled with improved corrosion resistance, may be had.

The effect of variations in nickel, copper and iron content have already been discussed. The carbon content may range from .01% to 2%, depending upon the use to which the alloy is to be put. I

Vhile excellent malleable alloys have been produced containing 03% carbon, a considerably higher content may be tolerated in the malleable grades. In general, increasing the carbon content increases the hardness of the alloy and also diminishes somewhat its cold workability. It is usually preferable to limit the carbon content to 30%; at .50% the precipitation of,graphite begins, which tends to diminish ductility; alloys intended to be malleable should contain less than 1%, but castings may contain up to 2% carbon.

A high carbon content does not materially affect the corrosion resistance. While high carbon alloys are restricted to castings, it is possible with ordinary precautions to obtain castings with as little as'.1 carbon.

These alloys, particularly with nickel contents from 25% to 35%, have a high electrical resistivity and are suitable for use in electrical devices in which the operating temperature does not exceed 500 C.

As a specific example of the properties common to the whole group, the alloy containing 29% nickel, 7% copper, 17% carbon, .8 manganese, is typical. This, in the hot rolled condition, has a proportional limit of 30,000 psi, an ultimate strength of 80,000 psi, an elongation of 44%, and a reduction of area of 68%. This alloy may be forged, hot rolled, cold rolled, cold drawn, machined without difiiculty by drilling, sawing and cutting in the lathe; it responds readily to welding with either the oxyacetylene flame or the electric arc, as well as to resistance or spot welding; it accepts solders and brazes readily; and is, in general, suited for use as an engineering alloy. Exposed ,to clean, salty, and smoky air, thin sheets have formed a tight. rusty surface coating but remain in good physical condition under conditions in failed by corrosion.

While a considerable variation in combiiron. A particular alloy containing 34% nickel, 6% copper, .2%.carbon, is. a good example suitable for use in exposed sheet metal work, as roofing, ventilators, stacks, cornices, skylight trim, etc., as well as heavier forms, such as in outdoor hardware.

It will now be appreciated that there has been provided an improved group of alloys comprising an iron-nickel base to which has been added copper in amounts ranging from 1% to 32%, the resulting products being distinguished by ready workability, ease of manufacture, and, under certain atmospheric conditions, characterized by the property of forming a tightly adherent corroded surface which appears to minimize or otherwise inhibit the propagation of the rust coating. In addition, the alloys of the present invention are characterized by the fact that, when exposed to dilute non-oxidizing acids, such as dilute sulphuric acid, they are relatively unattacked, and, when exposed to fresh-water sprays or the like, retain their original bright surface.

It will be observed that the present invention rovides an iron-nickel-copper alloy containingapproximately 26% to approximately 74% iron, approximately 25% to approximately 60% nickel, approximately 1% to approximately 12% copper, and'carbon exceeding approximately 0.25% up to about is produced which is l 2%, whereby an allo' wholly free from bar nodules and which has a substantially uniform softness.

It will also be noted that the present invention provides an iron-nickel-copper alloy comprising approximately 26% to approximately 74% iron, approximately 25% to approximately 60% nickel, approximately 1% to approximately 25% copper, nickel content being not less than 1.85 times the copper content to insure homogeneity of the alloy and carbon exceeding approximately 0.25% and extending up to about 2.0%, whereby an alloy is produced which is wholly free from hard nodules and which has a substantially uniform softness.

What I claim is 1. An alloy composed substantially of 26% to approximately 74% iron, approximately 25% to approximately 60% nickel, approximatel 1% to approximately 26% copper, the nickel content being not less than 1.85 times the copper content toinsure homogeneity, and carbon exceeding .40% and being under 2.0%, whereby an alloy isyproduced which is of substantially uniform softness.

easily worked and 2. An alloy composed substantially of 25% to approximately 60% nickel, approximately 1% toapproximately 12% copper, approximately 28% to approximately 74% iron, and carbon exceeding .40% and being under 2.0%, whereby an alloy is produced which is of substantially uniform softness.

3. An alloy composed substantially of 25% to approximately 40% nickel, approximately 1% to approximately 12% copper, approximately 48% to approximately 74% 1ron, and carbon exceeding 40% and beingunder 2.0% whereby an alloy is produced which is of substantially uniform softness.

4. Castings composed substantially of 26% to approximately 74% iron, approximately 25% to approximately 60% nickel, approximately copper. the nickel content being not less than 1.85 times the copper content to insure homogeneity, and carbon exceeding .60% and being under 2.0% whereby an alloy is produced which is of substantially uniform softness.

In testimony whereof I have hereunto set-my hand.

- NORMAN B. FILLING.

1% to approximately 26% 

